Someone

xrwma = [{'kx-'}, {'bo-'}, {'m*:'}, {'rv--'}];

X = [50 100 200 400 800];
Y = erwthma31(10);
pvin = 50:10:800
        
    figure
    hold on
    for N = 2:5
        pfout = polyfit(X, Y, N);
        pvout = polyval(pfout, pvin);
        plot(pvin, pvout, char(xrwma(N-1)));
        legend('N = 2', 'N = 3', 'N = 3', 'N = 4', 'Location', 'NorthWest', 'boxoff');
        xlabel('matrix size');
        ylabel('mean time');
        title('GER');
        hold off
    end